The present invention relates to a loop lifter, and more particularly to a loop lifter for continuous strip rolling mills.
In continuous strip rolling mills the rolled strip forms pendant loops between successive roll stands. For manufacturing reasons it is necessary to maintain these loops at a certain height and to maintain the strip tension as low and as constant as possible. For this purpose it is known to provide so-called loop lifters which engage the pendant loops from below and exert upwardly directed support for them. Such loop lifters have a pivotable arm provided at one end portion thereof with a so-called loop-lifting table in which a roll is journalled for free pivotable turning about a horizontal axis; it is this roll which engages the loop from below. The arm is made to pivot upwardly so that the roll engages the loop from below, by means of a drive. The construction of the drive is determined by three factors, namely the moment required for compensating the inherent weight of the loop lifter itself, the moment required for compensating the weight of the loop as it is pendant between two successive roll stands, and the moment required for compensating the strip tension. It is readily appreciable that the moment required to compensate the inherent weight of the loop lifter amounts to a substantial portion of the drive moment required for effecting the upward pivoting of the arm.
One known construction of a loop lifter utilizes a lever or arm which is pivotable in a fixed pivot point and which carries the aforementioned roller for engaging the loops from below. It is also known to provide a loop lifter in which an attempt has been made to reduce the swing moment of the loop lifter by mounting the roll not in a pivotable arm, but instead in a carriage which can be moved in vertical guides. In all prior-art loop lifters the engagement of the roll with the respective loops is effected either by means of hydraulic cylinders, pneumatic cylinders for electric motors which pivot the arm or move the carriage. To avoid fluctuations in the strip tension, which causes variations in the thickness and width of the strip being formed, the swing moments of the loop lifter itself, and the drive for the loop lifter, must be maintained as small as possible. Small swing moments for the drives can be obtained if hydraulic or pneumatic drives are used, but the exact regulation of the drive torque is possible in these types of drives. If an electric motor is used to drive the loop lifter, then the drive torque can be regulated very exactly but, on the other hand, the swing moments of the drive, particularly if a transmission is arranged between the motor and the loop lifter, are very substantial.
Another proposal that has been made in the art is to reduce the motor torque in loop lifters which utilize electric motors for their drive, by compensating for the weight of the roll and the arm carrying the same via a counterweight. Although this does not reduce the motor torque, it does not reduce the total swing moment and this measure is therefore also not fully satisfactory.